Recovery of zinc values by selective flotation of sulfide ores



W. A. BATES Filed Nov. l, 1949 RECOVERY OF ZINC VALUES BY SELECTIVE FLOTATION OF SULFIDE ORES April 29, 1952 ATTORNEYS Patented pr. 29, 11952 RECOVERY F zINo VALUES BY sELEc'rivii FLoTA'rIoN oF sULFIDE omis William A. Bates, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application November 1, 1949, Serial No. 124,873

8 Claims.

This invention relates to the recovery of zinc sulfide from sulfide-type ores. More particularly, it relates to the recovery of zinc sulde from polymetallic sulfide-type ores by a process of selective froth notation. Still more particularly, this invention relates to the recovery of zinc sulfide from ores in which zinc sulfide is associated with lead sulfide and pyrtes.

The ores in which zinc values occur in the form of sulfide may be subdivided into three broad classes: (l) Straight zinc ores in which Zinc sulnde is the only valuable metalliferous mineral, the remainder being quartz, limestone or other non-metalliferous gangue; (2) copper- Zinc sulfide ores in which copper sulfide and zinc sulfide are the valuable metalliferous components; and (3) lead-zinc sulfide ore in which Zinc sulfide and lead sulfide are the valuable metalliferous minerals. This latter type of orethe lead-zinc sulfide ore-is by far the most important in the mineral dressing industry. Therefore, while my invention generally relates to 'the recovery of Zinc sulfide from any sulfide-type ore, one of its particularly preferred ramifications is directed to the recovery of zinc sulfide from lead-zinc sulde ores.

The aforementioned three types of sulfide ores generally contain considerable amounts of pyrites in addition to quartz or other non-sulfide gangue. This admixture of pyrites may range from a few per cent to almost one hundred per cent of the gangue in the ore. In addition, small but economically attractive amounts of gold and silver are frequently present in the ore, and in the case of marmatitic ores some of the zinc in the zinc blende is found replaced by iron and manganese in -solid solution. l

` The separation of zinc sulfide from other components of sulfide-type ores by froth notation vtechniques is not a simple operation, as almost invariably at least two distinct concentrates must be produced. In the case of lead-zinc sulfide ores, the lead concentrate must be substantially completely freed from zinc contamination, while a number of economical and metallurgical considerations rule out the presence of an excess of pyrites in the zinc concentrate. First of all, because of the low unit value content of zinc sulnde in the zinc concentrate, the low grade of this latter occasioned by the presence of large amounts of pyrites increases considerably the costs of transportation to the smelter and can render the recovery of zinc from such a concentrate unproiitable. In the second place, presence of iron in the form of pyrites is known to have an adverse effect on the operation of retorts in the thermal type of smelter, while in the electrolytic plants for the reduction of zinc the presence of pyrites in the Zinc concentrate is apt to cause formation of insoluble zinc ferrites upon roasting, interfering with the recovery of zinc. In fact, difliculties are encountered in the treatment of practically all zinc-bearing sulfide-type ores, and are particularly annoying in the case of marmatitic ores which contain more than 10% pyrites.

Consequently, the discovery of new methods for beneciating and recovering zinc sulfide from sulfide-type ores by froth flotation, which would yield zinc concentrates of a higher grade than has heretofore been obtained with vsulfhydrictype collectors, e. g., with xanthates, is highly desirable.

I have found that zinc sulfide concentrates of improved grade can be recovered from sulfidetype ores by the application of a new and effective collecting agent of the cationic type. This collecting agent, referred to hereinafter in this specication as petroleum nitrogen bases, represents a complex mixture of alkyl and polyalkyl nitrogen-bearing heterocyclic compounds produced in the thermal treatment (pyrolysis) of petroleum. Ordinarily crude petroleum, and especially the California crude mineral oil, contains a certain proportion of heterocyclic nitrogen-bearing compounds of an unknown and complex structure, which in the course of refining of the various petroleum fractions are pyrolyzed to mixtures of lower molecular weight heterocyclic nitrogen-bearing compounds known among the refiners as the petroleum nitrogen bases.

The exact composition of these mixtures is not known; however, they are believed to contain appreciable amounts of alkylated homologues of pyridine and quinoline. Among the various operations of petroleum refining, the cracking of naphthas represents one of the largest sources of formation of these petroleum nitrogen bases. Whether originating in cracked naphthas, or in gas oils, or in other fractions of petroleum, the usual procedure of recovering the nitrogen bases therefrom consists in agitating the petroleum fraction with dilute sulfuric acid of about 30-50% strength, or with other suitable acid of appropriate strength, separating an acid layer containing the nitrogen bases from an oil layer, and neutralizing the acid layer. The recovered nitrogen bases range in color from yellow (when freshly recovered) through red to black liquids (on settling and exposure to air). They are basic in character and possess the specific odor of heterocyclic nitrogen compounds of the pyridine and quinoline series. They consistl essentially of a mixture of nitrogen-bearing alkylated heterocyclic com- 4 bases employed as collectors in the froth flotation of sulfide-type ores permits of securing highgrade Zinc concentrates low in lead and iron contents.

pounds boiling between about 120 F. and about 5 While all mixtures of petroleum nitrogen bases 630 F., approximately 75% coming over at about boiling between about 120 F. and about 630 F. 510 F. Low-boiling petroleum fractions upon are applicable in froth flotation of sulfide ores as thermal treatment yield W-boiling mixtures of selective collectors for zinc sulfide, those derived nitrogen bases of a correspondingly low average from cracked naphthas are found to be particumolecular Weight, and conversely higher boiling 10 larly effective. These preferred nitrogen base colpetroleum fractions yield higher boiling mixtures lectors for zinc sulde are essentially mixtures of of nitrogen bases of a higher average molecular alkylated homologues of pyridine and quinoline Weight. The individual components in these miX- with molecular Weights ranging from about 130 tures of petroleum nitrogen bases may range from to about 180 and even higher, as shown in Table I. monoand dimethyl pyridines to compounds as The application of petroleum nitrogen bases complex as C1sH25N; but, in any event, the moas collectors for froth flotation and recovery of lecular weights of these COrnpOllndS are higher Zinc sulde from sulfide-type ores in accordlfharl the molecular Weights 0f the Corre-Spending. ance with the present invention is rather mineral oil fractions o1 Cracked naphthas from straight-forward and does not call for a radical which they have been derived. go departure from the conventional technology of The complexity o1- the composition of nitrogen differential or selective froth flotation. Crude bases becomes clearly apparent upon considering zinc sulde ore, e. g., sphalerite, is ground in the distillation data (ASTM) in Table I, obtained water and made into an aqueous ore pulp, theA on a representative 500 cc. sample derived from particle size of the ground ore ranging from. 35 cracked naphtha. 5 mesh at the maximum to as low as 200i mesh.

TABLE I Gravity P P Per ourNo. Temp. F. oeenrt oeolit 'cept 24. P. 1. sp. or. C H

distilled; those, of Example B have been distilled. TABLE II Example A B Gravity A. P. I. (ASTM/D-287) 11.6 14.2 Specific Gravity 00/60F 0. 9888 0.9712 Flzsh Point (Cleveland Open Cup F.) ASTM/D- 10 Water by distillation, per cent. Solubility in 30% H1304, per cent Neutralization No., mgm. HzSOl/g Color, ASTM (ASTM `Dl55) I have discovered that petroleum nitrogen bases, when used as collectors in the froth otation of sulfide-type zinc-bearing ores, are highly selective and display an unusual collecting power for zinc sulde, but have practically no collecting eiect withrespect to pyrites and galeria. This unexpected selectivity' of petroleum nitrogen` To permit the recovery of zinc valuesfrom a straight zinc sulfide ore pulp, or, in the case of a polymetallic sulfide-type ore, from the tailing from a previous lead sulfide -or copperv sulfide flotation step, this-pulp or tailing is conditioned to establish alkalinity in the circuit, the pI-I being preferably of the4 order ofl from 7.0--to 11.0.

This desired alkalinity is secured by employing a pH regulator such as lime, sodium hydroxide, a suitable silicate or phosphate (e. g., sodium silicate or trisodium phosphate). However, soda ash is generally preferred for the purpose. If lime is used to impart alkalinity, it will be added in amounts not exceeding 1 pound per ton of ore. When soda ash is employed toregulate the pH of the circuit. as much as 3A pounds of soda ash per ton. of ore, and even greater quantities if necessary, will be added. In all cases. flotation will be effected at a pH of from about 7.0 to about 11.0. the optimum value. depending on the nature of the ore being treated. Thus, sphalerite is usually floated at a pH comprised between 7.0 and 8.5. On the other hand, marmatite is floated best at a pH ranging from 10.3 to 11.0.

In accordance with the usual practice of flotation of zinc sulfide, it should be adequately activated With copper Sulfate pentahydrate,

` (CuSO4.5H2O) which is added to thepulp in` amounts ranging from 0.5 to 1.5 poundslper-'tonoffthefore. Conventionalfrothers may-also be used, forrinstance, cresylic acid, pine oiliaridiavhe-.lilreL collector for zinc sulfide inamounts which de, pendron the grade. i. e., thefzinc contentv ofi the ore. Ordinarily, amounts .from 0.01.to.0,.5 pound perl ton of ore arefound to secureI high grade zince sulfide concentrates. The additonof the various conditioningreagents is4 preferably effected in a special conditioningI vessel r tankV at a relatively high dilution of the pulp. ofthe order of about 20. to 40%;V solids byfweight of` the pulp, though in some-instancesvthe pH regu.- lator may be added tothe grinding circuitand the collector may be introduced direcilyIlT/o:thel flotationcell. The conditioning treatment usually occupies from to 30 minutes or more, the` optimumduration being readily ascertainable. by the operator.

When treating a zinc-bearing ore;l containing lead sulde. this latter-willbeseparated; from zinc sulfide, pyrtes and othergangue; by; a conventional froth otationwith a` sulfhydricvtype collector, suchv as axanthate, iirst'deactivating and depressing zincA sulfide; and pyrites with sodium cyanide. and then. recererineby-otationfwith the sulfhydric collector a-lead sulfide concenetrate and a deleaded tailings Thisftailingjslconditioned with copper sulfate to reactivate zinc sulfide which is thenffloated away-with theaid of petroleum nitrogen-bases; as,L the collector.

The original lead-Zinc sulfide ore`A pulpy is; adjusted to the desired pH from about 7.0 to* about 11.0. Sodium cyanide is added to depress pyrites and to deactivate zincsulfide in amounts ranging from 0.1 to 0.5l pounds per tonof ore. If necessary, it may bereplaced by calcium cyanide, or potassium cyanide. In many instances, zince sulfate in amounts frcm x0;1= to 2.0 pounds per ton of ore is'added asan,4 aidin deactivating zinc sulfide by virtueof a4 synergistic commonion eiiect. Should theprebereXCeptionally clean, particularly when it is free from copper, conditioning with sodium cyanide willA become unnecessary. Conventional frothers, suchas crevsylic acid or pine oil; are alsogadded; if necessary. All of these various reagents are added intol a conditioning tank or conditioner, except for the IpH regulator, such `as lime or soda ashmentioned hereinbefore, which, in some cases, may be added into the-grinding-circuit. A' sulfhydric type collector, e. g., sodiumsecondary butylxanthate or sodium dithiophosphate` (,Aerofloat) in conventional amounts, fr om0.01n to 0.5 pound per ton of ore isaddedtosthe conditioner--after other reagents. Conditioning-takes rfrom 5 to 30 minutes or more, whereupon the" pulp is sub,- jected to flotation. Lead sulfide froth isskimmed off, and the deleaded*` tailingis-treated1ina second conditioner to readjust the fpH, if necessary, and to reactivate zinc'suldefWith-copper'sulfate as described hereinabove. The pH is adjusted by adding NazCOe or NaOH, depending on whether the pulp is too alkali-neor-not. Upon theaddition of petroleum nitrogen-base selective collector, and after sufficient conditioning- (5-30 minutes or more) zinc sulfide isgiioatedgaway in `the notation cells, while pyrites. and jgangue, are car.- ried off as tailings.

When handling zinc-:bearingoresfcontaining copper sulfide, goodrecoverieslwill be yobtained by following the general procedureoutlined hereinabove for lead-zinc. sulfide.ores, namely: cOppBl.

sulfide will be iioated away in an alkaline circuit Petroleum. nitrogen bases will be employed. as the selective with the. aid of' well-knowncollectors of; sulfihydric type, after having deactivated` andy defpressed zinc sulfide and pyrites with sodium cyanideand zinc sulfate; thereupon copper sulL- fate will be added to the copper-freetailingvzto reactivate zinc sulfide which will then be ,floated away with the petroleum nitrogen-base collector in accordance with the invention.

However, the preferred procedure in treatingav zinc-bearing ore containing copper sulde is to. form an alkaline pulp of asuitable-pI-I (e. g.; 7.0 to 11.0), to depressor deactivate: zinc sulfide and pyrites with sodium cyanide, with or without an addition of zinc sulfate as .may bezrequired by the nature of the ore, and to float the copper` sulfide with the aid of petroleum nitrogen bases, preferably in an amount from about. 0101 to: about'v 0.5 pound per tonof` the ore. The deactivated zinc sulfide in the copper sulfide tailing is7 thenreactivated with copper: sulfate and, upon. flota.-l tion with petroleum nitrogen` bases as indicated hereinbefore, a high grade zinc sulfide concentrate will be-separated from the gangue,

Where the ore to be treated contains zinc;sul.. nde, copper sulfideand lead sulde-in amounts which would justify the recovery of eachof them,

the preferred procedure will be to-form an alkaf line ore pulp, tocondition thispulp by 'depressing'. zinc sulfide and pyrites. with sodium cyanide and zinc sulfate, as described, and to.. float away a..

froth containing lead and copperwith the :aid-of a conventional sulfhydrictypecollector.. The.

lead-copperV sulfide froth may thenv be ,treatedin any known manner to separate-:lead from. copper, whereas thelead-free and copperf-free tailing is conditioned with copper sulfate toxreactivatezinc suliide and t0 float away the zinc: withY the` aidl of nitrogen bases as kthe selective ,collector for` zinc sulfide in accordancewith the invention.

The operation vof the process of thisinvention will be better understood from the following'step,+V by-step description of thefrecoveryof zincisulfide from a typical lead-zinc marmatitic sulfidey ore; as illustrated by the flow diagramzof the process' in the attached drawing.V

In the drawing, the lead-zincY sulfideitypeoreris fed to the process'frcm mine l and-lis subjectedto crushing first in coarse 'crusher A2,andthenfin fine crusher 3, whence itis dumpedxinto storage bin 4. From this binthe ore is drawn'outtoebe ground in thepresence of water, forrinstancein a ball mill 5; in this grinding operation, the .fore is reduced to the desired particle size, and converted into an aqueous ore pulp which issentto classifier 6; the oversize particles of theore in the pump are returned from this classifier to` ball mill 5, while the undersize particles proceed to conditioner I0 where they are conditionedprior to the notation of lead sulfide. The ore vpulp, is brought to the desired pH, which may be,. for instance, from about '7 to about 9.5, by the=addi tion of lime or of soda ash tothe circuit,ether at conditioner I0 or at ballv mill 5`. The..pH.regu-, lating reagent precipitates any, extraneous i iron ions likely to have formed by theoxidation of. pyrites, as well as lead. andcopper ions which would otherwise activate V.zinc sulfideand, cause its fioatation simultaneously with galeria. To depress pyrites and to deactivate zinc sulde, sodium cyanide is admitted into the pulpV under going the conditioning treatment in conditioner I0. If necessary, zinc sulfate is added. into conditioner I0 as lan aid in deactivating'zinc,sulfide. as well as conventional frotherssuch.ascresylic acid or pine oil." A collecting agentoftlie sulffhydric type, such as sodium or potassium ethyl;

isopropyl or butyl xanthates, or sodium diethyl dithiophosphate (sodium Aerofloat), is introduced into conditioner I in desired amounts. The action of sulfhydric collector may be augmented by the addition of a small amount of creosote oil. The conditioning treatment occupies from five to thirty minutes or more. After leaving conditioning vessel I0, the ore pulp passes to rougher lead flotation cells I I, where it is agitated and aerated, releasing a froth containing lead sulfide. This froth is then sent to cleaner lead notation cells I2, while the final lead concentrate from cleaner lead flotation cells I2 is passed through a vacuum filter I3 into a storage bin I4 to await its shipment to the smelter. The presence of the vacuum filter is optional, and it may be omitted. The cleaner tailings from cleaner lead flotation cel1 I2 may be recirculated either to conditioner I0 or to rougher lead flotation cells II.

The rougher lead tailings leaving cleaner lead flotation cells II enter conditioning vessel 20 where the deleaded ore pulp is conditioned prior to the flotation of zinc sulfide with the aid of petroleum nitrogen bases as the selective collector. The pulp is conditioned for about iive to thirty minutes. If lime is present to an excess, soda ash may. be added to precipitate lime and to maintain the desired pH. Should the alkalinity be too low as a result of the lead flotation treatment, sodium hydroxide may be used to raise the pH. Reactivation of zinc sulfide is secured by the addition of copper sulfate as herein before described. The conditioning agents, i. e., the pH regulator and the copper sulfate activator, are added together into conditioner 20, simultaneously with or immediately followed by the collecting agent for zinc sulfide.

This agent, in accordance with the invention, is constituted by petroleum nitrogen bases in amounts ranging from 0.01 to 0.5 pound per ton of ore, depending on the zinc content or grade of the ore. Usual frothing agents similar to those used in the lead circuit may also be employed. However, the amount of frother required will be considerably smaller than the amounts commonly used with sulfhydric collectors, since petroleum nitrogen bases are found to be frothing agents per se. From conditioner 20, the ore pulp is passed into rougher zinc flotation cells 2 I, whence the froth is passed into cleaner zinc flotation cells 22, yielding a nal concentrate which, upon filtering through vacuum filter 23, is stored in storage bin 24 to await shipment to the smelter. Filter 23 is optional and may be omitted. The tailing from the rougher Zinc flotation cell is withdrawn to the reject pond. The tailing from cleaner zinc flotation cell 22 may be recirculated, either to conditioning vessel 20 or to rougher zinc flotation cells 2 I.

In the application of selective froth flotation in accordance with the present invention, the employment of petroleum nitrogen bases as the collector for Zinc sulfide is found to reduce the requirement for copper sulfate activator of zinc sulfide by as much as two-thirds as compared with the amounts of this activator required when employing sulfhydric collectors for the same purpose.

A particularly important consequence of the application of petroleum nitrogen bases as the collector for the selective froth flotation of zinc sulfide is the superior grade of zinc concentrates obtained thereby, as will be seen from the following examples:

Example I .-This example is a typical case of the selective froth flotation of a marmatitic ore, employing petroleum nitrogen bases as the collector for zinc sulfide in the zinc circuit. The ore pulp fed to the lead circuit contained 7.5 per cent of zinc and 18 per cent of iron as pyrites. After the recovery of lead by flotation with a sulfhydric collector, e. g., a xanthate, the deleaded pulp contained about 22 per cent by weight of solids, and the pH thereof was less than 9.0. Two parallel flotation runs were made with this deleaded pulp-one (B) using petroleum nitrogen bases as the collector for zinc, and the other (A) using sodium secondary butyl xanthate to collect zinc. Other reagents employed in these two runs in addition to the collectors for zinc sulfide were the following:

Lbs. per ton Lime, added at the ball mill, to secure alkalinity Sodium cyanide, added at the ball mill, to depress zinc sulfide and pyrites in the lead Petroleum nitrogen bases as the collector for zinc sulfide in Run B (average molecular weight of about -165) 0.11

The results of the two runs are presented in Table III.

TABLE III Cleaner Rougher Concentrate Concentrate Per Cent Per Cent Recovery Rejection Per Per Per Per Zn Fe Cent Cent Cent Cent Zn Fe Zn Fe RunA 41.6 17.0 17.5 31.2 84.6 44.9 RunB.. 52.2 11.7 40.5 14.4 84.0 89.0

These results definitely indicate that the employment of petroleum nitrogen bases as the collector in the flotation of zinc sulfide yields a concentrate of a greatly superior grade as compared with the concentrate obtained with a xanthate-type collector, while the recovery of the zinc mineral is practically the same in both runs.

Example IL In this series of tests, a marmatitic ore'containing lead sulfide, zinc sulfide and pyrites was ground substantially entirely through 65 mesh and diluted with Water to 35% solids. The ore pulp was then conditioned with the following reagents added into the conditioner in the order of their tabulation:

Lbs/ton of ore Lime 2.0 Sodium cyanide 0.15 Sodium secondary butyl xanthate 0.08 Pine oil 0.5

The conditioning treatment lasted five minutes, and the pH of the ore pulp was brought to 11.0. After recovering the lead concentrate by froth flotation with a xanthate collector, as described hereinbefore in this specification, the lead concentrate was found to be equal to 8.4% of the weight of the original ore feed. It contained 4.45% of 9 zinc. Two runs, C and D, were then made to recover zinc sulfide from the lead tailing. In run C, soda ash was used to maintain alkalinity, in the amount of 3 pounds per ton of ore. In run D,

the same amount of soda ash was used with an l addition of lime in the amount of 1 pound per ton of ore. In both runs C and D, 0.8 pounds per ton of copper sulfate was employed to reactivate zinc sulfide., The pH of run C was 10.3, that of run D was 11.3. In run C, 0.2 pounds of petroleum nitrogen bases per ton of ore was used to collect zinc sulfide, while 0.08 pounds of petroleum nitrogen bases per ton of ore was used to collect zinc sulfide in run D. These nitrogen bases had an average molecular weight of about 160-165. The conditioning treatment occupied approximately five minutes. In a comparison mill run E, the following reagents were used: Sodium secondary butyl xanthate as the collector for zinc sulfide in an amount of 0.59 pounds per ton of ore, lime in the amount of 3.7 pounds per ton of ore to secure a pH of 12.0, and copper sulfate in an amount of 1.87 pounds per ton of ore to activate zinc sulnde.

The results of runs C, D and E are given in Table IV, as follows:

TABLE IV Run Run Run Weight of Zn in cleaner Zn concentrate in per cent of original feed 24. 4 23. 4 22. l Per cent Zn in cleaner Zn concentrate 52. 53.0 (l) Per cent Zn in cleaner Zn telling..- 4.85 Q. 4 Per cent Zn in rougher Zn tailing 0. 77 0 90 0.79 Ier cent Zn in origin ed 13.7 13.8 12.0 Recovery of Zn in per cent of original iced 93, 0 89. 7 92. 6

l About 50.0.

Eample III .-The high selectivity of petroleum nitrogen bases as the collector for zinc sulfide at a pH of the pulp of less than 8.0 can be seen from the following data obtained from the runs F and G on a rather difficult lead-Zinc sulfide ore constituted by a fine-grained intergrowth of galena and marmatite and a pyrrhotite gangue. In this instance, the ore is first ground to a moderately fine grind (about 50% passing through a 20G-mesh screen), and as much of the ne lead and zinc-free gangue as possible is eliminated in the first flotation stage. Two 500 g. samples of -mesh ore are ground for 10 minutes in a ball mill in the presence of 300 cc. of water, and the resulting pulp conditioned first with 1.0 pounds of Ca(OH 2 and 0.2 pound of NaCN per ton of the ore. It is transferred to a flotation cell where it is further conditioned for 5 minutes with sodium isopropyl xanthate (0.04 pound per ton of ore) and a mixture of 85% coal-tar creosote and cresylic acid (0.09 pound per ton of ore). Upon flotation of the lead froth, in both runs, the pulp is conditioned in the cell with copper sulfate pentahydrate (1.0 pounds per ton of ore) for about 5 minutes. In run F, 0.05 pounds of sodium diethyl dithiophosphate per ton of the ore is used as the collector, supplemented by 0.2 pounds per ton of ore of cresylic acid frother. After conditioning for 3 minutes, the pulp having a pH of '7.4 is passed to the flotation cell and a zinc froth skimmed off. In-Run G, in lieu of dithiophosphate, 0.09 pounds of petroleum nitrogen bases per ton of the ore is added as the selective collector (average molecular weight of about 1GO-165), the cresylic acid frother being unnecessary since petroleum nitrogen bases furnished suiiicient froth. The pH of the conditioned pulp is '7.5. The recovery of Zn with the dithiophosphate collector in Run F is equal to 54.0%, the ligure obtained with petroleum nitrogen bases in Run G is 55.7%. The zinc concentrate grade obtained with petroleum nitrogen bases is equal to 32% and is strikingly superior to that secured with the dithiophosphate (24.6%), proving the high selectivity of petroleum nitrogen bases. Only '7.4% of the iron is present in the Zinc concentrate secured with petroleum nitrogen bases as compared with 12.7% Fe obtained with dithiophosphate.

I have found petroleum nitrogen bases just as selective and more powerful than sodium or potassium ethyl and butyl xanthates when employed as collectors for the froth flotation of zinc sulfide. They are likewise more effective and just as selective as the sodium diethyl dithiophosphate collector employed in the past to separate zinc sulfide from pyrites. Lower-boiling fractions of petroleum nitrogen bases are more selective toward zinc sulfide (and copper sulfide) than the higher boiling fractions but are less powerful collectors than these latter. In actual practice, it is preferred to employ mixtures containing both low and high boiling fractions, i. e., mixtures distilling between about to about 630 F., with 75% coming over at about 510 F., to secure effective collection of zinc values from the ore pulp.

It is to be understood that the invention described hereinabove with reference to petroleum nitrogen bases derived from cracked naphthas is operativewith all equivalent petroleum nitrogen bases derived from other fractions of petroleum in the course of refining, e. g., from the so-called SO2 pearl extract, various gas oil fractions, etc.

In fact, the invention may be successfully practiced by employing other equivalent nitrogen bases of heterocyclic structure as may be obtained, for instance, by shale-oil or coal-tar distillation, by synthesis, and as by-products of various industrial processes.

My new process based on the application of petroleum nitrogen bases as the selective collector for the flotation of zinc sulfide is not limited to the examples or to the flow diagram presented hereinabove. The remarkable results secured by the employment of this collecting agent extend generally to other types of sulfide ores in which zinc sulfide is present. Thus, one practicing the invention may vary the quantities of the various reagents to suit', the requirements of each pai'- -ticular case and the nature of each particular ore. The rougher zinc concentrate may be cleaned and recleaned as many times as one may wish. In addition, other collectors, p-I-I regulators, depressors, deactivators, activators, and frothers which will not interfere with the selective action of petroleum nitrogen bases as the selective collector for zinc sulfide may be used in the aforedescribed process without departing from the scope of the present invention, which includes all the modifications and variations of 11 said process except as limited in the appended claims.

I claim:

1. A process for the recovery of zinc sulfide from a sulfide ore containing zinc sulfide in admixture with pyrites and non-sulfide gangue, which comprises effecting froth flotation of a pulp of said ore in an alkaline circuit having a pH from about '7.0 to about 11.0 in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogenbearing compounds boiling between about 120 F. to about 630 F. as the selective collector for zinc sulfide, and separating a froth of beneficiated Zinc sulfide from a tailing containing pyrites and non-sulfide gangue.

2. A process for the recovery of zinc Vsulfide from lead-zinc sulfide ore which comprises the steps of forming a pulp of said ore having a pH from about 10.3 to about 11.0; conditioning said pulp to deactivate and to depress zinc sulfide and pyrites therefrom; effecting froth flotation of said pulp vin the presence of a sulfhydric collector; collecting a lead sulfide froth anda deleaded tailing; reactivating zinc sulfide in said deleaded tailing with copper sulfate; subjecting said deleaded tailing containing said reactivated zinc sulde to froth fiotation in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogenbearing compounds boiling between about 120 to about 630 F. and being present in an amount from about 0.01 to about 0.5 pound per ton of ore; and recovering a froth containing beneficiated zinc sulfide.

3. A process for the recovery of zinc sulfide from a zinc-copper sulfide ore which comprises the steps of forming an alkaline pulp of lsaid ore; deactivating and depressing zinc sulfide and pyrites therefrom; effecting froth fiotation of copper sulfide in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogen-bearing compounds boiling between about 120" F. and about 630 F. as the collector for copper sulfide; reactivating zinc sulfide in the copper-free tailing from said flotation with copper sulfate; effecting froth flotation of said tailing inthe presence of Aa mixture of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogen-bearing compounds boiling between about 120 F. to about 630 F. as the selective collector for zinc sulfide; and recovering a froth containing beneficiated zinc sulfide.

4. A process for the recovery of zinc sulfide from a zinc-copper sulfide ore which comprises the steps of forming an alkaline pulp of said ore; deactivating and depressing zinc sulfide and pyrites therefrom; effecting froth flotation of copper sulfide in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogen-bearing compounds boiling between about 120D F. to about 630 F. as the selective collector Vfor copper sulfide, said nitrogen bases being present in an amount from about 0.01 to about 0.5 lb. per ton of the ore; reactivating zinc sulfide in the copperfree tailing from said fiotation with copper sulfate; effecting froth flotation of said tailing in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogen-bearing compounds boiling between about 120 F. to about 630 F., said nitrogen bases being present in an amountfrom about 0.01 to about 0.5 pounds per ton of the ore; and

1'2 recovering a froth containing beneficiated zinc sulfide.

5. A process for the recovery of zinc sulfide from a sulfide ore containing zinc sulfide in admixture with iron sulfides and non-sulfide gangue, which comprises effecting froth flotation of a pulp of said ore in an alkaline circuit having a pH from about '7.0 to about 11.0 in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogen-bearing compounds boiling between about F. and about 630 F. as the selective collector for zinc sulfide, and separating a froth of beneficiated zinc sulfide from a tailing containing iron suldes and non-sulfide gangue.

6. A process for the recovery of zinc sulfide from a. sulfide ore containing sphalerite in admixture with iron sulfides and non-sulfide gangue, which comprises effecting froth otation of a pulp of said ore in an alkaline circuit havving a pH from about 7.0 to about 11.0 in the presence of petroleum nitrogen bases consisting essentiallyof a mixture of alkylated heterocyclic nitrogen-bearing compounds .boiling between about 120 F. and about 630 F. as the selective collector for zinc sulfide, and separating a froth of beneficiated sphalerite from a tailing containing iron sulfides and non-sulfide gangue.

'7. A process for the recovery of zinc sulfide from a sulfide ore containing sphalerite in admixture with pyrites and non-sulfide gangue, which comprises effecting froth flotation of a pulp of said ore in an alkaline circuit having a pH from about 7.0 to about 11.0 in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogenbearing compounds boiling between about 120 F. and about 630 F. as the selective collector for zinc sulfide, and separating a froth of beneficiated zinc sulfide from a tailing containing pyrites and non-sulfide gangue.

8. A process for the recovery of zinc sulfide from a marmatitic ore containing zinc sulfide, iron sulfides and non-sulfide gangue, which comy prises effecting froth flotation of a pulp of said ore in an alkaline circuit having a pH from about 7.0 to about 11.0 in the presence of petroleum nitrogen bases consisting essentially of a mixture of alkylated heterocyclic nitrogenbearing compounds boiling between about 120 F. and about 630 F. as the selective collector for zinc sulfide, and recovering a froth of beneficiated zinc sulfide from a tailing containing iron sulfides and non-sulfide gangue.

WILLIAM A. BATES.

REFERENCES CITED The following references are of record in the .file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Mining and Metallurgy, August 1936, pp. 386- 389, article by R. A. Pallanch, entitled Factors Governing the Separation of Lead and Zinc in Ore vby Flotation. 

1. A PROCESS FOR THE RECOVERY OF ZINC SULFIDE FROM A SULFIDE ORE CONTAINING ZINC SULFIDE IN ADMIXTURE WITH PYRITES AND NON-SULFIDE GANGUE, WHICH COMPRISES EFFECTING FROTH-FLOTATION OF A PULP OF SAID ORE IN AN ALKALINE CIRCUIT HAVING A PH FROM ABOUT 7.0 TO ABOUT 11.0 IN THE PRESENCE OF PETROLEUM NITROGEN BASES CONSISTING ESSENTIALLY OF A MIXTURE OF ALKYLATED HETEROCYCLEC NITROGENBEARING COMPOUNDS BOILING BETWEEN ABOUT 120* F. TO ABOUT 630* F. AS THE SELECTIVE COLLECTOR FOR ZINC SULFIDE, AND SEPARATING A FROTH OF BENEFICIATED ZINC SULFIDE FROM A TAILING CONTAINING PYRITES AND NON-SULFIDE GANGUE. 